In forming a fine pattern of an electronic device such as a semiconductor device (integrated circuit or the like) and a liquid crystal display device, a transfer method is used where a pattern of a mask or a reticle, on which a pattern to be formed is formed by proportionally magnifying by about four to five times thereinafter, generally referred to as “reticle”), is reduced on an object to be exposed such as a wafer by using a projection exposure apparatus.
The projection exposure apparatus has shifted its exposure wavelength to a shorter wavelength side in order to cope with microfabrication of circuit patterns associated with higher integration of a semiconductor device (integrated circuit). Currently, as the wavelength, 248 nm of KrF excimer laser and 193 nm of ArF excimer laser being shorter wavelength are mainly used.
In the projection exposure apparatus, with shorter wavelength of exposure wavelength, light quantity of flare caused by fine polishing residue or flaw left on the surface of optical members (such as lens and mirror) constituting a projection optical system and light quantity of flare generated due to the unevenness of a lens material have become a problem. The flare is local flare that appear in the vicinity of the edge of the image of a light-shielding pattern on an image plane and a global flare spreading outside the local flare.
Particularly, the local flare varies depending on the density of a pattern being a focus of attention regarding the flare quantity of its vicinity, and OPE (Optical Proximity Effect) characteristics is affected thereby.
Flare measurement in the projection optical system of a projection exposure apparatus is currently performed by a method called an “exposing method”, in which a pattern for flare measurement formed on a reticle for measurement is actually transferred onto a resist layer on a wafer via the projection optical system (refer to Patent Document 1 for example).
In the exposing method, for example, an Eth/E0 method is known in which a square light-shielding mark whose one side is d, as shown in FIG. 17 is used as a flare measurement mark, and a ratio (Eth/E0) between optimum exposure quantity Eth where a resist image (an image of a mark formed on the resist layer on a wafer surface after the wafer is developed, which is obtained by transferring the flare measurement mark onto the resist layer of the wafer, becomes a predetermined size and excessive exposure quantity E0 where the resist image is completely disappeared is used as an index of flare. Note that the ratio (Eth/E0) by the exposing method should be called as a contrast value C hereinafter.
In the Eth/E0 method by the exposing method a line pattern may also be used as disclosed in Patent Document 1. In addition, as a method of flare measurement by the exposing method, a line width measurement method is also known in which the line width of a resist image of a predetermined mark for measurement (line-and-space mark, for example) is used as the index of flare.
However, in the flare measurement by the above-described exposing method, since it is necessary to go through a development process or the like of the object be exposed such as the wafer, the measurement requires a long period of time, and the flare measurement is one of the causes of reduction of throughput in a series of processing in the projection exposure apparatus. Further, because a measurement process of resist image is included, if environment in a coating process of resist, a development process or the like is varied, this might affect the measurement values of the resist image, and highly accurate flare measurement may become difficult.
[Patent Document 11] Kokai (Japanese Unexamined Patent Application Publication) No. 2003-318095